Electrofishing for razor clams trial: update - February 2021 to January 2022

8. Other Work Streams

A PhD project (in collaboration with the Scottish Association of Marine Science - SAMS) which studies the organism and ecological impacts of electrofishing in Scottish shallow coastal habitats continued into its second year. Initial progress was severely impeded by the COVID-19 pandemic, making access to laboratories and other resources particularly difficult. However, progress resumed following the easing of restrictions. The project seeks to advance understanding in three areas:

• examining the long-term physiological performance of organisms exposed to electrical fields
• investigating whether there are any detectable adverse effects of experimental electrofishing on benthic communities in the field
• analysing background data on the trial electrofishery

Data gathered for this PhD project came from razor clams sent to SAMS by fishers. Age was determined by counting the number of visible annual growth rings on the external surface of the shell, then the internal rings are counted from shell cross-sections using a microscope. These aging counts will be validated using oxygen isotope analysis to ensure the correct ring structures are being identified and counted. Future work will include combining age and size data to generate growth curves for each site sampled. Fitting growth curves using mixed models will allowrazor clamgrowth rates to be compared between different fishery areas around the Scottish coast.

Shore crabs (Carcinus maenas) are currently the model organism being used in experiments looking at long term effects on physiology on non-target fauna. An electrical fishing rig has been set up in aquaria for use in tank-based experiments using both razor clams and shore crabs. After an approximate two-minute exposure period to the electric field, physiological metrics of stunned and control animals are tracked over time in order to assess the medium- to long-term impact of stunning upon organism functioning. This includes tracking metabolic rate using custom built flow through respirometry apparatus.

Alongside lab-based work, plans are being developed, subject to available funding, for field work to study the benthic and infaunal communities which have been electrofished in order to gain a better understanding of the effects of the current trial electrofishery upon seabed habitats.